Coupling Joint

Coupling Joint is formed by means of a coupling, which is a device for connecting parts together, and almost as diversified as joint itself. Amongst builders it usually takes the form of a hinge, union, screw shackle, fishplate, detached socket, collar, or sleeve, while pump-fitters use a key joint for coupling well-rods. Tension rods in roofs and horizontal bracing in bridges are usually regulated by screw shackles. Parts of wrought iron piles or pillars, when made in more than one length, are connected by a coupling-piece consisting of a short wrought iron or steel cylinder, which is slipped over the butting ends, as shown in Fig. 78, and bolted to both in cases where welding is not feasible, but great care is needful in the case of piles that the bolts and bolt holes are sufficiently firm and reliable to withstand the great twisting strain that will be brought upon them in screwing in.

Coupling Joint 79

Fig. 78.

Cover Joint

Cover Joint is a butt joint covered by a plate on one or both sides.

Cramp Or Cramped Joint

This is an alternative term for clamped joint.

Diagonal Joint occurs in riveted cylindrical iron structures, and is made by riveting the plates together when spirally arranged round the axis with which the joint forms an angle of 45°. It is shown in Tig. 79, and in the case of a boiler is one-fourth stronger than a longitudinal joint. The same term for want of a better is applicable to the connections of the diagonal bars of a girder with the flanges or booms. The joint may be made either with one large pin or two or more rivets, the latter being safest, but bolts or pins are compulsory with cast iron elements. Ornamental castings are employed to conceal the diagonal joints of roof trusses.

Double Nut Joint

Double Nut Joint is one formed with a nut and a back nut. Thus a suspending rod passing through a flattened tie-rod is often secured by a nut on both sides for purposes of adjustment.

Double Riveted Joint

A joint in ironwork formed by a double row of rivets through both plates either arranged as chain-riveting, Fig. 80, or as zigzag-riveting, Fig. 94. The plates may either overlap or be joined with cover strips or plates - that is, may either form a lap or butt joint - in which latter case there will be four rows of rivets; if but one cover be used, it must equal the main plates in thickness; but if two, then each must not be less than half the thickness of a main plate. The following gives a tolerably exact idea of what is necessary to insure equal strength against the crushing and tearing of the plate on the one hand, and the shearing of the rivet on the other; but in practice engineers have no absolutely uniform rule. In a double-riveted lap-joint the diameter of the rivet equals two thicknesses of plate, the pitch (or distance from centre to centre of rivets in the same row) is from 4 to 5 diameters, and the distance between the pitch lines (or lines through the centres of the rivets of each file or row) should be in zigzag-riveting two-thirds of the pitch, and in chain-riveting 2 diameters, the total lap for the two kinds being 5 and from 6 to 6 diameters respectively. In a double-riveted butt-joint the diameter of the rivet equals 1 1/8 the thickness of the plate, the pitch is 5 1/8 diameters, and the distance between the pitch lines in chain-riveting is 2 diameters, and in zigzag-riveting 3 diameters. Hence the width of the respective cover-plates is 11 and 13 diameters.

Double Riveted Joint 80

Fig. 79.

Double Riveted Joint 81

Fig. 80.